The present invention relates to polishing of surfaces, such as semiconductor wafers, and more particularly, to an advanceable polishing sheet arrangement for chemical-mechanical polishing devices.
In the process of fabricating modem semiconductor integrated circuits (ICs), it is necessary to form various material layers and structures over previously formed layers and structures. However, the prior formations often leave the top surface topography of an in-process wafer highly irregular, with bumps, areas of unequal elevation, troughs, trenches, and/or other surface irregularities. These irregularities cause problems when forming the next layer. For example, when printing a photographic pattern having small geometries over previously formed layers, a very shallow depth of focus is required. Accordingly, it becomes essential to have a flat and planar surface, otherwise, some parts of the platen will be in focus and other parts will be out of focus. In fact, surface variations on the order of less than 100 angstroms over a 25xc3x9725 mm die would be preferable. In addition, if the irregularities are not leveled at each major processing step, the surface topography of the wafer can become even more irregular, causing further problems as the layers stack up during further processing. Depending on the die type and the size of the geometries involved, the surface irregularities can lead to poor yield and device performance. Consequently, it is desirable to effect some type of planarization, or leveling, of the IC structures. Most IC fabrication techniques make use of some method to form a planarized wafer surface at critical points in the manufacturing process.
One method for achieving semiconductor wafer planarization or topography removal is the chemical-mechanical polishing (CMP) process. In general, the CMP process involves holding and/or rotating the wafer against a rotating polishing platen under a controlled pressure. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d pad or a fixed-abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad.
An effective CMP process not only provides a high polishing rate, but also provides a substrate surface which is finished (lacks small-scale roughness) and flat (lacks large-scale topography). The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad. The polishing rate sets the time needed to polish a layer, which in turn sets the maximum throughput of the CMP apparatus.
During CMP operations, the polishing pad needs to be replaced periodically. For a fixed-abrasive pad, the substrate wears away the containment media to expose the embedded abrasive particles. Thus, the fixed-abrasive pad is gradually consumed by the polishing process. After a sufficient number of polishing runs (e.g., forty to fifty) the fixed-abrasive pad needs to be replaced. For a standard pad, the substrate thermally and mechanically damages the polishing pad and causes the pad""s surface to become smoother and less abrasive. Therefore, standard pads must be periodically xe2x80x9cconditionedxe2x80x9d to restore a roughened texture to their surface. After a sufficient number of conditioning operations (e.g., three hundred to four hundred), the conditioning process consumes the pad or the pad is unable to be properly conditioned. The pad must then be replaced. An advantage of fixed-abrasive polishing pads is that they do not need to be conditioned.
In the CMP process, the polishing pad may be attached to the platen surface with an adhesive. Significant physical effort is often required to peel the polishing pad away from the platen surface. The adhesive then must be removed from the platen surface by scraping and washing with a solvent. A new polishing pad can then be adhesively attached to the clean surface of the platen. While this is happening, the platen is not available for the polishing of substrates, resulting in a decrease in polishing throughput. The use of fixed-abrasive pads, which need to be replaced more often than standard polishing pads, result in an even further decrease in polishing throughput. Thus, although the fixed-abrasive pads do not need to be conditioned, the use of fixed-abrasive pads in a CMP apparatus results in a higher cost of operation.
An aspect of the present invention is a chemical mechanical polishing apparatus, comprising:
a platen having a flat planar major surface, said platen being rotatable about an axis normal to said major surface;
a polishing sheet releasably secured to a top of said major surface of said platen to rotate with said platen, said polishing sheet extending over said top of said major surface of said platen and having an exposed surface for polishing a substrate; and
a hydrophobic layer for substantially preventing aqueous liquid which penetrates under said polishing sheet from wetting a lower surface of said polishing sheet.
A further aspect of the present invention is a method of chemical mechanical polishing, the method comprising the steps of:
bringing a substrate into contact with a polishing sheet extends over a top major surface of a platen, wherein a hydrophobic layer for substantially preventing an aqueous liquid which penetrates underneath said polishing sheet from wetting a lower surface of said polishing sheet is positioned between said polishing sheet and said top major surface of said platen;
releasably securing said polishing sheet to said platen;
rotating said platen to rotate the polishing sheet and create relative motion between said substrate and said polishing sheet;
releasing said polishing sheet from said platen; and
incrementally advancing said polishing sheet in a linear direction across said top major surface of said platen after said polishing step has been completed.
Additional aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modification in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.